In telecommunications networks, for signalling purposes, different tone signals are exchanged between user equipment and network devices, such as telephones, switches, repeaters and radio access units or radio base stations in radio telecommunications networks.
An example of such a signalling tone signal is called “ringback tone signal”. This is the audible ringing that is heard by a calling party at user equipment in a telecommunications network after dialing and prior to the call being answered by the called party. This ringback tone assures the calling party that a ringing signal is being transferred to the called party.
Different from the ringing signal, which is produced by the user equipment of the called party to indicate an incoming call or message, the ringback tone signal is not generated by the user equipment of the calling party.
The ringback tone signal may be generated by a local switch of the telecommunications network serving the calling party or by a remote switch of the telecommunications network serving the called party, for example.
The type of ringback tone, i.e. the sound, duration and rhythm of the ringback tone signal, may differ in various countries. The ringback tone signal may be out of synchronization with the actual ringing signal heard by the called party. The ringback tone signal generally starts and stops when the actual ringing signal provided to the called party starts and stops.
Private Branch eXchanges (PBX), for example, may forward a tone signal to a calling party if the switchboard operator has put the call on hold to transfer the incoming call to a desired called party.
Other tone signals may be produced by data modems or the like connected to a telephone line, for example.
It will be appreciated that, if the received tone signal is produced at a remote switch of a called party, for example, by evaluating the quality of the received tone signal one may get an indication about the quality of the telecommunications link between the calling party and the remote switch or another network device that produces the tone signal.
In the event of a bad quality, for example, provisions can be made to switch to another transmission line providing a better transmission quality or to control the receiving user equipment or network devices involved in the communication, in order to improve the quality of the transmission link. In radio telecommunications systems, a measure to improve the radio link quality can be to increase the RF transmit power at the side of the telecommunications network or to increase the receiver sensitivity at the end user device, for example.
In another application, the quality data derived from the received tone signals is gathered and analysed in association with route information of the telecommunications line over which the tone signal is received. From this analysis, for setting up a call to a particular destination, routes or telecommunications lines providing an unacceptable quality can be excluded. The other way around, one may of course use the gathered quality information to select particular routes or telecommunications lines providing a desired quality. Note that the term “telecommunications line” includes both wired and wireless connections.